Flying the AW609: a preview
Editor's Note: This story appears as part of a comprehensive feature on AgustaWestland in the Dec'13-Jan'14 issue of Vertical. To read the digital version of the magazine, click here.
It has now been more than 20 years since the Bell-Boeing V-22 Osprey made its first flight, and five years since the aircraft entered operational service with the United States Marine Corps and Air Force. So, the tilt-rotor is no longer a new concept. However, a civilian pilot contemplating the AgustaWestland AW609 is likely to have a number of questions about the aircraft — one of those being, “What is it like to fly?”
To find out, I paid a visit in late September to AgustaWestland Tilt Rotor Company in Arlington, Texas, where the first prototype in the program is undergoing flight testing for basic envelope expansion (a second prototype is flying in Italy, while the third and fourth prototypes are under construction). No, I didn’t get to fly the actual aircraft, which had yet to be approved for demonstration flights. But I did get to fly the next best thing: the AW609 engineering simulator, which is being used to fine-tune changes to the flight control software and to flight test maneuvers before they’re performed in the real aircraft.
The AW609 engineering simulator lacks motion, along with some of the bells and whistles that will appear in a full-flight training simulator that should be available around the time of aircraft certification. Still, it’s comparable in sophistication to many of the flight training devices now being used for pilot training. According to AW609 program manager Clive Scott, it’s also quite realistic, thanks to the more than 850 hours of actual flight data accumulated by the program so far. “Now, with so many hours flying, the models are very representative,” he said.
My guide for the demo was AW609 test pilot Dan Wells, a retired U.S. Army airplane and helicopter pilot who began flying tilt-rotors in 2006, when he was loaned to the U.S. Air Force for its V-22 development program. He has now been in the 609 program for about two years, having followed it to AgustaWestland from his previous employer, Bell. “I just love the aircraft and I love the program,” Wells said, expressing enthusiasm over the program’s renewed momentum. “We’re starting to get the mentality that we’re going to certify this thing.”
The first thing I noticed upon climbing into the simulator’s cockpit was that, as a helicopter pilot, I felt right at home. That’s because the AW609 has conventional helicopter flight controls: a cyclic-like center stick, yaw pedals and, notably, a left-side collective lever rather than the throttle-like thrust control lever found on the V-22. (For a comprehensive overview of flying the V-22, see p.108, Vertical, Feb-Mar 2012.) Is this the ideal control configuration? I’m not sure, especially given the flexibility embodied in the AW609’s triply redundant, fly-by-wire flight control system. Regardless, the arrangement is sure to be a selling point for helicopter pilots, who will find the transition to the AW609 to be that much simpler.
Similar to the V-22, the AW609 has three distinctive modes of flight, defined by the position of the nacelles. The aircraft is in “VTOL” (vertical take-off and landing) mode when the nacelles are between 85 and 95 degrees (with 90 degrees being the full vertical position, and 95 degrees being the maximum aft position, used for decelerating the aircraft or hovering with a tail wind). “Conversion” mode encompasses nacelle positions from 85 degrees down to zero, with the proprotor blades at 100 percent r.p.m. “Airplane” mode occurs when the nacelles are at zero degrees tilt, and proprotor r.p.m. is at 84 per cent.
I commenced my simulator flight with a lift off to a hover, which was much like any helicopter lift off. At this point, the nacelle position was 87 degrees: typical, Wells said, for no-wind hovers. The hover was quite stable, and the aircraft performed much like a helicopter through a few hovering turns (in VTOL mode, the flight control system controls yaw by tilting the proprotor discs differentially; this changes to differential pitch control as the aircraft enters airplane mode).
From my location over an airport runway, I then performed a normal take-off, which I initiated by holding a nacelle control switch on the collective forward until it stopped automatically at 75 degrees (these pre-set nacelle angles are another way in which the AW609 differs from the V-22, and make the aircraft safer and easier to fly). The aircraft began moving forward and climbing. As I gained altitude, I began the transition to airplane mode: first, a click forward on the control switch to set the nacelles at 50 degrees, another click to set them at zero degrees, and a final click to drop the r.p.m. to 84 per cent. At this point, we were up and away, and the aircraft was flying much like a turboprop airplane, with a maximum cruise speed of 275 knots.
After maneuvering the aircraft in airplane mode for a while, I turned it back to the virtual airport to fly some traffic patterns. As I approached the airport, clicking backward on the nacelle control switch first restored the proprotor r.p.m. to 100 percent, then moved the nacelles to 50 degrees, then moved them back to 75 degrees (although not all at once: each step in the conversion process requires that the aircraft be within a specific airspeed range, which is indicated to the pilot on the instrument panel). As I set up a traffic pattern, I began slowing the aircraft to around 60 knots as I rolled out on final, bringing the nacelles to 80, then 85 and finally 87 degrees. Without yet having a good feel for the deceleration process — how much of it owed to nacelle position, and how much to cyclic position — I didn’t aim for my landing spot too precisely. However, I brought the aircraft to a hover over the runway fairly easily, and without incident.
After a quick set down and pick up, I then performed another normal takeoff, but instead of transitioning to airplane mode, flew a traffic pattern in conversion mode, with the nacelles at 50 degrees. This felt a lot like flying a helicopter in a traffic pattern at a moderate airspeed. Instead of a normal approach to a hover, I brought the aircraft in for a running landing, touching down at around 40 knots and 85 degrees nacelle position. After landing, I moved the nacelles to their full aft position of 95 degrees (then began rolling backward before remembering to restore the nacelles to 87 degrees).
To wrap things up, I performed a rolling takeoff with the nacelles at 75 degrees, and re-entered the traffic pattern. That pattern concluded with perhaps the most interesting maneuver of the day: a steep approach initiated at 60 knots and 300 feet above ground level (AGL). With the nacelles set to 95 degrees, and the cyclic stick held forward, we were tilted nose-down and looking straight down at the runway for most of the approach. The visibility was incredible — far better than in most helicopters, which have a nose-high attitude on approach. I began leveling the aircraft at around 100 feet AGL, again bringing it to a stable hover.
One thing I didn’t get to experience was an autorotation, as AgustaWestland was still in the process of developing autorotation procedures for the aircraft (at press time, the company told me that these autorotation tests were progressing effectively). According to Wells, if the aircraft experiences a complete power failure, an emergency conversion switch will allow the nacelles to quickly be moved to vertical to enter an autorotative descent. Loss of a single engine is less dramatic, as the AW609’s interconnected drive train allows power from the remaining engine to be shared between the proprotors (and a “soft stop” on the collective will adjust automatically to allow the pilot to pull more power). Developing one-engine inoperative (OEI) procedures for the aircraft is another to-do item for the flight testing program, which will be facilitated by an OEI training mode on the aircraft’s new flight control software.
That flight control software is the real magic of the AW609: it calculates and compensates for most of the aerodynamic complexity associated with transitioning from vertical to highspeed forward flight. That may make some pilots nervous, and it certainly means that the software’s developers have their work cut out for them. The result, however, is shaping up to be a very intuitive aircraft with a highly manageable learning curve. “I think the biggest thing I want people to take away from it is how easy it is to fly,” remarked Wells. “Any helicopter pilot can get in the 609 and fly it right away.”